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Updated description of DOT and friends to account for optional GLOBAL

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Salvatore Filippone
2018-04-20 15:57:26 +01:00
parent eaaa701c2e
commit 4a6c0857f1
281 changed files with 15338 additions and 14268 deletions
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@@ -23,26 +23,26 @@
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@@ -110,10 +110,10 @@ dot \leftarrow x^H y
<P>
<PRE>
psb_gedot(x, y, desc_a, info)
psb_gedot(x, y, desc_a, info [,global])
</PRE>
<BR><P></P>
<DIV ALIGN="CENTER"><A NAME="1978"></A>
<DIV ALIGN="CENTER"><A NAME="2010"></A>
<TABLE>
<CAPTION><STRONG>Table 2:</STRONG>
Data types</CAPTION>
@@ -215,7 +215,20 @@ Type: <B>required</B>
Intent: <B>in</B>.
<BR>
Specified as: an object of type descdata<TT>psb_desc_type</TT>.
</DD>
<DT><STRONG>global</STRONG></DT>
<DD>Specifies whether the computation should include the
global reduction across all processes.
<BR>
Scope: <B>global</B>
<BR>
Type: <B>optional</B>.
<BR>
Intent: <B>in</B>.
<BR>
Specified as: a logical scalar.
Default: <code>global=.true.</code>
<BR>
<P>
</DD>
<DT><STRONG><B>On Return</B></STRONG></DT>
@@ -230,7 +243,8 @@ Specified as: an object of type descdata<TT>psb_desc_type</TT>.
SRC="img21.png"
ALT="$y$"></SPAN>.
<BR>
Scope: <B>global</B>
Scope: <B>global</B> unless the optional variable
<code>global=.false.</code> as been specified
<BR>
Specified as: a number of the data type indicated in Table&nbsp;<A HREF="#tab:f90dot">2</A>.
</DD>
@@ -247,30 +261,55 @@ An integer value; 0 means no error has been detected.
</DD>
</DL>
<P>
<BIG CLASS="LARGE"><B>Notes</B></BIG>
<OL>
<LI>The computation of a global result requires a global
communication, which entails a significant overhead. It may be
necessary and/or advisable to compute multiple dot products at the same
time; in this case, it is possible to improve the runtime efficiency
by using the following scheme:
<BR>
<IMG
WIDTH="500" HEIGHT="73" ALIGN="BOTTOM" BORDER="0"
SRC="img27.png"
ALT="\begin{lstlisting}
vres(1) = psb_gedot(x1,y1,desc_a,info,global=.false.)
vres(...
...,y3,desc_a,info,global=.false.)
call psb_sum(ictxt,vres(1:3))
\end{lstlisting}">
<BR>
In this way the global communication, which for small sizes is a
latency-bound operation, is invoked only once.
</LI>
</OL>
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